I don't know it's architecture but I am willing to bet there is a fat ass server somewhere that does most of the work ... Listen if all you need is the vibe I can do that, but if we are going to discuss architecture it is not going to be any different than a big server with API, just multiple servers with the same API, basically AppViews or whatever you want to call it, but it is just big things that need to make money somehow because it can't be made cheap.. yes. You can donate to it... But it is a big server somewhere and it needs to be compliant and at least sustainable financially.